Two-stage countercurrent leaching process for the recovery of phosphates, yttrium and rare earth values

ABSTRACT

Phosphates and yttrium and rare earth metal values are recovered from solid materials, particularly phosphate ores or commercial concentrates and especially apatites, in a two-stage leaching process comprising a first extraction with an aqueous acid solution to remove part of the phosphate and a substantial part of the yttrium and a second extraction with stronger acid to remove the residual phosphate, yttrium and rare earth values, then recovering the products from the first and second extracts. The process is carried out in a countercurrent manner by using the aqueous acid solution from the second extraction, after partial removal of yttrium and rare earth values, in the first extraction.

United States Patent Coltrinari et al.

[4 1 Mar. 7, 1972 [54] TWO-STAGE COUNTERCURRENT LEACHING PROCESS FOR THERECOVERY OF PHOSPHATES, YTTRIUM AND RARE EARTH VALUES [72] Inventors:Enzo L. Coltrinari; James K. Kindig, both v[21] Appl. No.: 881,742

[52] Cl. ..23/18, 23/19 R, 23/22, 23/23, 23/24 R, 23/312 ME, 23/165,23/105, 23/ 107 [51] Int. Cl. ..C22b 59/00 [58] FieldofSearch ..23/15,19, 18,22,23, 165 C, 23/107, 312 ME; 75/115, 121

[56] References Cited UNITED STATES PATENTS 2,425,573 8/1947 Soddy..23/19 R X 2,860,031 11/1958 Grinstead ..23/15 W 1,351,489 8/1920 Ryan..23/19 X 2,849,286 8/1958 Welt et al ..23/19 X OTHER PUBLlCATlONS Shawet al. US. Atomic Energy Commission Report ISC- 407," declassified Feb.26, 1957, pp. 1, 8- 10, 22, 24- 26, 28, 30- 32.

Primary Examinerl-lerbert T. Carter Attorney-M0rgan, Finnegan, Durham &Pine [57] ABSTRACT Phosphates and yttrium and rare earth metal valuesare recovered from solid materials, particularly phosphate ores orcommercial concentrates and especially apatites, in a twostage leachingprocess comprising a first extraction with an aqueous acid solution toremove part of the phosphate and a substantial part of the yttrium and asecond extraction with stronger acid to remove the residual phosphate,yttrium and rare earth values, then recovering the products from thefirst and second extracts. The process is carried out in acountercurrent manner by using the aqueous acid solution from the secondextraction, after partial removal of yttrium and rare earth values, inthe first extraction.

7 Claims, 2 Drawing Figures TWO-STAGE COUNTERCURRENT LEACHING PROCESSFOR THE RECOVERY OF PHOSPHATES, YTTRIUM AND RARE EARTH VALUES Thisinvention relates to the recovery of phosphates and metals from solidmaterials. More particularly, it concerns recovery of phosphates andyttrium and rare earth values from solids such as ores, commercialresidues, and the like, especially, calcium phosphate, i.e., apatite,solids and particularly apatite-containing tailings from magnetite ironore concentration plants.

Yttrium, a metal produced by the instant process, is valuable for anumber of uses, for example, as a getter in vacuum tubes and in theproduction of yttrium hydride as a neutron moderator. The rare earthsprovided by this invention are primarily those of the lanthanide series,illustrative members of which are lanthanum, cerium, praseodymium,neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium;erbrium, thulium, ytterbium and lutetium. The various salts of the rareearths have different colors and are suitable as pigments. The forms ofphosphates produced as products of the instant invention have a numberof uses. For example, the reaction product with ammonia, diammoniumphosphate, is an important fertilizer.

BACKGROUND OF THE INVENTION The phosphate minerals, and especiallyapatite, are widespread and available, for example, in sedimentaryrocks. One specific source of apatite comprises tailings from magnatiteiron ore concentrating plants. This apatite contains yttrium and rareearth values in concentrations substantial enough to be of interest as asource of these elements if a commercially feasible recovery methodcould be provided. Apatite of this type, of course, also containssubstantial quantitles of phosphate which if it could be recoveredeconomically would be valuable commercially, for example, as mentionedabove, as a source of phosphoric acid or for ammonium phosphatefertilizers. A number of methods are known in the art to recoverphosphates, yttrium and rare earth values from solid materials. However,for a variety of reasons, none of the obvious prior art methods appearsto be technically or economically feasible for this type of apatiteconcentrate. A number of preliminary laboratory experiments indicatedthat relatively expensive methods such as acid treatment and ionexchange recovery or physical benefication methods were not preferred. Amethod of flotation concentration followed by acid leaching, however,did show promise. The use of acid treatment of solid materials as afirst step to extract phosphates and metal values is a matter of commonknowledge and experience. See, for example, the disclosure in US. Pat.No. 2,860,031. Moreover, superphosphate is conventionally produced on avery large scale by the leaching of phosphatic rock with sulfuric acid.As employed herein, the term leaching" is intended to indicate that afluid aqueous phase is employed to effect direct removal of metal value(or of a phosphate) from a solid substance. Since the most effi' cientof these processes utilize sulfuric acid to dissolve the phosphaticminerals, it is clear that in the selection of a commercial process theacid consumption and the price of sulfuric acid will be very importantfactors in the cost of recovery of the products. Furthermore, tomaintain the consumption of reagents at the lowest possible level, andto keep the size of the equipment small with respect to the amount ofsolid material to be processed, consideration should also be given toconcentrating the solid mineral before the recovery operation is begun.Techniques to prepare the mineral and to concentrate it are known in theart. For example, if it is desired to increase the amounts of phosphateand metal values in apatite, it is useful to subject the solid tocrushing or grinding, to desliming and to concentration, e.g., byflotation with a fatty acid, all in accordance with known techniques. Asis mentioned hereinabove, the cost of sulfuric acid can be a substantialfacselected could employ less expensive acid, for example, the

so-called black spent sulfuric acids from oil refinery operations, whichare available at a substantially lower price than fresh sulfuric acid,this would be a very important contribution to the commercialfeasibility of the process. Leaching of the phosphatic ore or commercialconcentrates with sulfuric acid provides an extract containing dissolvedphosphate, yttrium and rare earth values. A number of prior an methodsare available to remove the metals from the extracts, among which one ofthe most important is solvent extraction, such as with monoor di-octylphosphate or orthophosphates. See US. Pat. Nos. 2,860,031; 2,955,913 and3,167,402. It is also known that, if, as is necessary, an excess ofordinary commercial sulfuric acid is used to dissolve the phosphate,yttrium and rare earth values in apatite ores or concentrates, it isnecessary to raise the pH of the extract with, for example, lime orlimestone, before the extract is fed to the solvent extraction system,if yttrium is to be removed most effectively. In addition to the addedcost of purchasing and handling lime or limestone, this stepprecipitates gypsum which must be removed from the solvent extractionfeed in a clarifyer. If there could be provided a means to avoid addinglimestone, a substantial advantage in process economics would result. Ithas now been found, surprisingly, that if the leaching process of theprior art is modified substantially, being run in two countercurrentstages, the need to add limestone to adjust the pH is obviated; theamount of strong sulfuric acid needed in the process is reduced; andrecovery of yttrium and rare earth values at a higher pH can beachieved; moreover, impure, inexpensive sulfuric acid can be employedinstead of expensive strong sulfuric acid and the amount of acidconsumption in the process is significantly reduced.

It is accordingly an object of the present invention to provide animproved means to recover phosphates, yttrium and rare earth values fromsolid materials, including ores and concentrates.

It is a further object of the invention to provide an improved means torecover phosphates, yttrium and rare earth values from apatite minerals.

Still another object of this invention is to provide a means to recoverphosphates, yttrium and rare earth values from apatite concentrationsmore economical in its use of sulfuric acid than heretofore.

Still another object of the instant invention is to provide an improvedmeans to recover phosphate, yttrium and rare earth values from apatite,without the need to neutralize excess sulfuric acid with limestone.

DESCRIPTION OF THE INVENTION The above valuable objects, and additionalobjects apparent to those skilled in the art from a consideration of thedescription herein, are easily achieved by practice of the presentinvention which is:

In a two-stage, countercurrent process for recovering phosphate, yttriumand rare earth metal values from a solid material, the steps comprisinga. leaching said material with an aqueous solution containing dissolvedphosphate and excess sulfuric acid in an amount sufficient to produce afirst acid leach solution containing part of the phosphate and asubstantial part of the yttrium values from said material and separatingsaid first acid leach solution from the leached residue;

b. leaching the residue from step (a) with water and sulfuric acid in anamount sufficient to produce a low pH second acid leach liquorcontaining almost all of the residual phosphate, residual yttrium andrare earth values from said material and separating said second acidleach solution from the leached residue;

c. recovering a portion of the yttrium and rare earth values from low pHsecond acid leach liquor from step (b), so that during recycling of saidsecond acid leach liquor into step (a), the solubility of the yttriumand rare earth salts will not be exceeded but the phosphate content ofthe solution will be raised to a level sufficient to permit economicextraction of the phosphate; and

d. extracting the yttrium and rare earth values from the first acidleach liquor from step (a). dividing the extracted liquor and sendingone portion for recovery of the contained phosphate and the otherportion to the second stage leach, step (b).

A useful pH range for the first acid leach solution [step (21)] is fromabout 0.50 to about 1.0. and preferably about 0.7. This will provide forremoval of a substantial part. i.e.. more than about 50 percent byweight of the contained yttrium. A useful pH range for the low pH secondacid leach liquor" is from about 0.02 to about 0.25. and preferablyabout 0.05. Recoveryin step (c) contemplates preferably asolvent-extraction technique. as will be described hereinafter.

lPreferred features of this invention are:

A process wherein the solid material is an apatite concentrate.

A process wherein the solid material comprises apatite tailings from amagnetite iron ore concentration process which have been concentratedsubsequently by flotation to contain by analysis about 15-25 percent Pand about l).25l .5 percent yttrium.

A process wherein the sulfuric acid used in step (b) is an impure. blackacid. containing organic residues formed by contacting petroleumfractions with substantially organic residuel'ree sulfuric acid.

A process according to the invention including the step oftlefluorinating the aqueous solution.

Another preferred process is one wherein the yttrium and rare earthvalues are recovered by solvent extraction from the separated acid leachsolutions from steps (a) and (b).

litill another preferred process includes the step of splitting saidaqueous. yttrium and rare earth extracted solution from the first andleach step to) into two portions. using the first portion in step (a)and recovering the phosphate from the second portion.

Special mention is made of a particularly valuable embodiment of theinvention which is a two-stage. countercurrent process for recoveringphosphates. yttrium and rare earth values from a concentrated solidapatite material containing, by analysis about percent P 0 about 0.7percent yttrium and about 3 percent total rare earths, all percentagesby weight. comprising a. leaching said material with a solutioncontaining dissolved phosphate and excess sulfuric acid at a temperatureof from about to about C. to produce a first acid leach solution of pH0.7 containing part of the phosphate and a substantial part of theyttrium values from said material. thickening and then separating saidfirst acid leach solution from the leached residue;

b. leaching the thickened residue from step (a) with an aqueous solutioncontaining sulfuric acid at a temperature of from about 30 to about 35C. to produce a second. strong acid leach solution of pH about 0.05containing the residual phosphate. yttrium and rare earth values.filtering said second acid leach solution from the leached residue anddiscarding said residue;

p. solvent-extracting a portion of the yttrium and rare earth valuesfrom the second, strong acid leach solution of step (b). defluorinatingand recycling said solution into step (a); and

d. solvent-extracting the yttrium and rare earth values from the firstacid leach solution from step (b). dividing said solution into twoextracted portions. and using the first portion as part of said aqueoussolution in step (b) and recovering the phosphates from the secondextracted portion.

As is mentioned above. the portion of yttrium and rare earth valuesremoved during step (c) will be such that on recycle of extractedmaterial into step (a) the solubility of yttrium and rare earth saltswill not be exceeded although the phosphate content will be raised to alevel justifying economic recovery. leg. about 50 grams/liter or more.

When used herein and in the appended claims. the term "caching" is usedas defined above. The term recovering" is used in its broadest sensewithrespect to phosphate. recovery can be made in any art-recognized manner,e.g., concentration into a form of phosphoric acid or production ofdiammonium phosphate by reaction with ammonia followed bycrystallization or granulation. Yttrium and rare earth values arerecovered." e.g., by ion exchange techniques, or, preferably, byliquid-liquid solvent extraction" techniques in which the leach liquoris contacted with a solvent selective for the metal values which isimmiscible with the liquor and which consists of a suitable amine oralkyl phosphate dissolved in an oil or hydrocarbon solvent. The twophases are separated and the metal values recovered from the organicphase, e.g., by the use of a mineral acid stripping operation. See thedisclosure of 0.8. Pat. No. 3.167.402. The term black acid contemplatesa so-called waste sulfuric acid from petroleum refineries. This 15 astrong acid which contains organic residues (petroleum sulfonates)formed by contacting petroleum fractions with substantially organicresidue-free sulfuric acid to sweeten them. The term defluorinating"contemplates adding a reagent. such as a sodium salt. e.g., sodiumnitrate. or sodium carbonate, or a calcium salt, e.g., calciumcarbonate, to precipitate fluoride. Defluorination may be necessary whencrystallization is not used. to produce a feed liquor of sufficientpurity to yield. upon ammoniation and granulation, a satisfactorydiammonium phosphate.

DESCRIPTION OF THE DRAWINGS A more complete understanding of the presentprocess will be understood from the following discussion with referenceto the drawings in which:

FIG. 1. is a flowsheet illustrating the process of the invention; and

FIG. 2. is a flowsheet illustrating the process of the invention showingsemischematically the equipment used to carry the initial feed ofapatite concentrate through leaching, filtration and recovery of thevaluable constituents from the first and second leach solution.

The process will be described broadly with reference to FIG. 1. The oreor commercial residue is first crushed or ground to the desired sizeand. optionally, may be concentrated, e.g., by flotation with fattyacid. Concentration can be useful with apatites from magnetite iron oreprocessing because these tailings contain usually only about 5-6 percentP 0 and 0.2 percent Y. The crushed phosphate-containing material next ismixed in the FIRST STAGE LEACH with a solution containing dissolvedphosphates and an excess of sulfuric acid. This solution is obtainedfrom the SECOND STAGE LEACH passing it first through a first Y+RE EX-TRACTOR and. optionally, through a defluorination step. This latterrecycle is the countercurrent feature of this invention. After thematerial has been leached, the mixture is transferred to a THICKENER.The effluent portion of the slurry rich in phosphates and yttrium isseparated. optionally clarified in a FILTER (the solids being returnedto the FIRST STAGE LEACH) and, passed through a Y+RE EXTRAC- TOR andthen a portion is processed to remove the phosphates therefrom. Thesolids from the THICKENER are transferred to the SECOND STAGE LEACH andtreated with water. the remaining portion of Y+RE extracted liquor fromthe first acid leach and strong sulfuric acid to dissolve residualphosphate. yttrium and rare earth values. After completion of leaching.the mixture is transferred to the FILTER and the tailings (gypsum andinsolubles) are separated and discarded. The leach solution is processedfor recovery of yttrium and rare earth values in a second Y+REEXTRACTOR. and then sent through an optional DEFLUORINATOR back to theFIRST STAGE LEACH. A stripper is shown, which can be employed to recoverY and RE values from the solvent extracts.

The process will be described more specifically with reference to aspecific embodiment and FIG. 2. As is shown in FIG. 2. the crushed solidmaterials are fed to the first stage leaching tank where they are mixedand agitated with a solution containing a considerable quantity ofdissolved phosphates and excess sulfuric acid for from about 4 to 6hours, at about 30-35 C. to produce a first acid leach solution. Themixture then is transferred to a leach thickener tank from where theoverflow rich in phosphates and yttrium is removed, transferred to aclarifying filter and then to solvent extraction equipment (SX) wherethe metal values are extracted with one portion to be subsequentlyutilized in the second stage leach and the remainder sent to phosphaterecovery. The underflow from the leach thickener tank, having a solidscontent of about 50 percent is transferred to second stage leachingwhere the slurry, still containing appreciable phosphate values isagitated and water, a portion of the (SX) extracted liquor from thefirst stage leach described above, and strong sulfuric acid are added todissolve residual phosphate and other values. This stage requires about4-6 hours at 3035 C. and the preferable pH is low, e.g., 0.02 to 0.25.The material is transferred to a leach extractor with the tailings beingdiscarded as waste. The extract is transferred to a solvent extractorprocessing equipment (SX) and the metal values are removed: The Y and REextracted liquor is then transferred to the first stage leach afterpassing through an optional defluorinator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following exampleillustrates the process of the instant invention.

EXAMPLE An aqueous solution (pilot plant leach liquor) that contained123 g./l. phosphate as P 1.6 g./l. yttrium (Y), 8.3 g./l. fluoride (F)and had a pH of 0.25 was solvent extracted (with 15 percent by volumedi-2-ethy1hexyl phosphoric acid- 85 percent by volume kerosene, twostages, phase ratio o/a, 1.5/1, minutes contact); the raffinatecontained 122 g./l. P 0 0.004 g./l. Y, 8.5 g./l. F and had a pH of 0.22.The fluoride analysis of the solution was lowered from 8.5 g./l. to 4.0g./l. by addition of sodium nitrate (NaNO and a solid and liquidseparation made. I

The aqueous solution from the above steps was then combined with aground apatite flotation concentrate that contained 21.3 percent byweight of P 0 and 0.76 percent yttrium (Y) in a first stage leach andthe slurry was agitated for 6 hours at 3035 C. and 18.9 percent solids.

A solid and liquid separation was made and the resulting solutioncontained 134 g./l. P 0 0.66 g./l. Y, 4.8 g./l. F and had a pH of 0.73;this solution was solvent extracted for Y and rare earths (three stages,above conditions) and after extraction the aqueous solution contained133 g./l. P 0 0.004 g./l.

I Y, 4.6 g./l. F and had a pH of 0.63. Part of the phosphate isrecovered. The residue from this first acid leach solids and liquidseparation contained 14.2 percent P 0 and 0.35 percent Y.

These solids, residue from the first leach, were then releached in asecond stage with an aqueous solution, composed of black acid, water andaqueous solution from the first acid leach after the same was solventextracted to remove the yttrium rare earths, pH 0.05, for 6 hours at3035 C. A solid and liquid separation was made on this second, strongacid leach and the residue or tailings contained only 1.93 percent P 0and 0.10 percent Y. The aqueous strong acid leach liquor contained 126g./l. P 0 0.84 g./l. Y, 6.8 g./l. F and had a pH of 0.05. This can berecycled into the first stage leach after being solvent extracted anddefluorinated as described above.

The combined phosphate recovery was 89.1 percent and the Y recovery was84.2 percent.

The acid consumed, black sulfuric, was 2.6 pounds (100 percent H perpound P 0 dissolved from the apatite flotation concentrate or 2.3 pounds(100 percent H S0 per pound P 0 contained.

In contrast to these results, a single-stage leaching process, notaccording to this invention, in which a more expensive, pure white acidwas used, required an acid consumption of 2.9 pounds (100 percent H SO)/pound P 0 dissolved or 2.7 pounds (H SO )/pound contained in theconcentrate.

In a similar, single-stage leaching process substituting the inexpensiveblack sulfuric acid used above, the acid consumption requirementsincreased substantially, to 3.5 pounds 100 percent H 80 per pound P 0dissolved or 3.3 pounds 100 percent H SO )/pound P 0 contained.

It can thus be seen that carrying out the process in accordance with thepresent invention provides a simple easy and economic technique forobtaining a high recovery of phosphate and yttrium and rare earth valuesfrom an apatite concentrate. In accordance with this invention from 80to 95 percent of the phosphate and from 80 to percent of the yttriumvalues may be recovered from the apatite concentrates.

While the invention is useful in connection with processing apatiteconcentrates and ores, it may also be used in processing various otherrare earth ore concentrates which correspond generally to apatite ores.

In view of the foregoing disclosure, the process of the invention can becarried out according to the example and disclosure set forth above orwith such variation and modification as will be readily apparent tothose skilled in the art.

Since certain changes may be made in carrying out the above methodwithout departing from the scope of the inven' tion, it is intended thatall matter contained in the above description should be considered asillustrative and not as limiting in any sense.

We claim:

1. In a two-stage, countercurrent process for recovering phosphates,yttrium and rare earth metal values from a solid material, the stepscomprising a. leaching said material with an aqueous solution containingdissolved phosphate and excess sulfuric acid in an amount sufficient toproduce a first acid leach solution containing phosphate and yttriumvalues from said material and separating said first acid leach solutionfrom the leached residue;

b. leaching the residue from step (a) with water and sulfuric acid in anamount sufficient to produce a second acid leach liquor with a pH ofabout 0.02 to about 0.25 containing the residual phosphate, residualyttrium and rare earth values from said material and separating saidsecond acid leach solution from the leached residue;

c. recovering the yttrium and rare earth values from the second acidleach liquor from step (b). by contacting said leach liquor with anorganic immiscible solvent therefor which comprises a suitable amine oralkyl phosphate dissolved in an oil or hydrocarbon solvent, so thatduring recycling of said second acid leach liquor into step (a), thesolubility of the yttrium and rare earth salts will not be exceeded butthe phosphate content of the solution will be raised to a levelsufficient to permit extraction of the phosphate; separating theresulting organic phase containing yttrium and rare earth metal valuesfrom the aqueous acid phase and recycling the aqueous acid phase to step(a); and

. extracting the yttrium and rare earth values from the first acid leachliquor from step (a) by contacting said leach liquor with an organicimmiscible solvent therefor which comprises a suitable amine or alkylphosphate dissolved in an oil or hydrocarbon solvent, separating theorganic phase from the aqueous phase, dividing the aqueous phase andsending one portion for recovery of the contained phosphate and theother portion to the second stage leach, step (b).

2. A process as defined in claim 1 wherein said solid material is anapatite concentrate.

.3. A process as defined in claim 1 wherein said solid materialcomprises apatite tailings from a magnetite iron ore concentrationprocess which have been concentrated subsequently by flotation tocontain by analysis from about 15 to about 25 percent P and from about0.25 to about 1.5 percent of yttrium.

A. A process as defined in claim 1 wherein the sulfuric acid used instep (b) is an impure, black acid containing organic residues formed bycontacting petroleum fractions with sub- :stantially organicresidue-free sulfuric acid.

15. A process as defined in claim 1 including the step of defluorinatingsaid aqueous acid phase prior to recycling step ii a).

b A two-stage, countercurrent process for recovering phosphates, yttriumand rare earth values from an apatite-containing solid materialcomprising a. leaching said material with a solution containingdissolved phosphate and excess sulfuric acid. at a temperature of fromabout 30 to about 35 C.. to produce a first acid leach solution of pHabout 0.7 containing phosphate and yttrium values from said material.thickening and then separating said first acid leach solution from theleached residue;

leaching the thickened residue from step (a) with an aqueous solutioncontaining sulfuric acid at a temperature of from about 30 to about 35C. to produce a second strong acid leach solution of pH about 0.05containing the residual phosphate, yttrium and rare earth values.filtering said second, strong acid leach solution from the leachedresidue and discarding said residue;

. solvent-extracting a portion of the yttrium and rare earth values fromthe second, strong acid leach solution of step l b) by contacting saidleach liquor with an organic immispible solvent therefor which comprisesa suitable amine or alkyl phosphate dissolved in an oil or hydrocarbonsolvent, separating the resulting organic phase containing yttrium andrare earth metal values from the aqueous acid phase. defiuormating andrecycling the aqueous acid phase into step (a); and

pi. solvent-extracting the yttrium and rare earth values from the firstacid leach solution from step (b) by contacting liiald leach liquor withan organic immiscible solvent therefor which comprises a suitable amineor alkyl phosphate dissolved in an oil or hydrocarbon solvent,separating the organic phase from the aqueous phase. dividing theaqueous phase into two extracted portions, and using the first portionas part of said aqueous solution in step (b) and recovering thephosphates from the second extracted portion.

l. in a two-stage. countercurrent process for recovering phosphates,yttrium and rare earth metal values from apatite, the steps comprisinga. leaching said material with an aqueous solution containing dissolvedphosphate and excess sulfuric acid in an amount sufficient to produce afirst acid leach solution pontaining phosphate and yttrium values fromsaid material and separating said first acid leach solution from theleach residue;

. leaching the residue from step (a) with water and sulfuric acid in anamount sufficient to produce a second acid leach liquor with a pH ofabout 0.02 to about 0.25 containing the residual phosphate, residualyttrium and rare earth values from said material and separating saidsecond acid leach solution from the leached residue;

. recovering the yttrium and rare earth values from the second acidleach liquor from step (b), by contacting said leach liquor with anorganic immiscible solvent therefor which comprises a suitable amine oralkyl phosphate dissolved in an oil or hydrocarbon solvent, so thatduring recycling of said second acid leach liquor into step (a), thesolubility of the yttrium and rare earth salts will not be exceeded butthe phosphate content of the solution will be raised to a levelsufficient to permit extraction of the phosphate; separating theresulting organic phase containing yttrium and rare earth metal valuesfrom the aqueous acid phase and recycling the aqueous acid phase to step(a); and

d. extracting the yttrium and rare earth values from the first acidleach liquor from step (a) by contacting said leach liquor with anorganic immiscible solvent therefor which comprises a suitable amine oralkyl phosphate dissolved in an oil or hydrocarbon solvent, separatingthe organic phase from the aqueous phase, dividing the aqueous phase andsending one portion for recovery of the contamed phosphate and the otherportion to the second stage leach, step (b l.

x r r k

2. A process as defined in claim 1 wherein said solid material is anapatite concentrate.
 3. A process as defined in claim 1 wherein saidsolid material comprises apatite tailings from a magnetite iron oreconcentration process which have been concentrated subsequently byflotation to contain by analysis from about 15 to about 25 percent P2O5and from about 0.25 to about 1.5 percent of yttrium.
 4. A process asdefined in claim 1 wherein the sulfuric acid used in step (b) is animpure, black acid containing organic residues formed by contactingpetroleum fractions with substantially organic residue-free sulfuricacid.
 5. A process as defined in claim 1 including the step ofdefluorinating said aqueous acid phase prior to recycling step (a).
 6. Atwo-stage, countercurrent process for recovering phosphates, yttrium andrare earth values from an apatite-containing solid material comprisinga. leaching said material with a solution containing dissolved phosphateand excess sulfuric acid, at a temperature of from about 30* to about35* C., to produce a first acid leach solution of pH about 0.7containing phosphate and yttrium values from said material, thickeningand then separating said first acid leach solution from the leachedresidue; b. leaching the thickened residue from step (a) with an aqueoussolution containing sulfuric acid at a temperature of from about 30* toabout 35* C. to produce a second strong acid leach solution of pH about0.05 containing the residual phosphate, yttriUm and rare earth values,filtering said second, strong acid leach solution from the leachedresidue and discarding said residue; c. solvent-extracting a portion ofthe yttrium and rare earth values from the second, strong acid leachsolution of step (b) by contacting said leach liquor with an organicimmiscible solvent therefor which comprises a suitable amine or alkylphosphate dissolved in an oil or hydrocarbon solvent, separating theresulting organic phase containing yttrium and rare earth metal valuesfrom the aqueous acid phase, defluorinating and recycling the aqueousacid phase into step (a); and d. solvent-extracting the yttrium and rareearth values from the first acid leach solution from step (b) bycontacting said leach liquor with an organic immiscible solvent thereforwhich comprises a suitable amine or alkyl phosphate dissolved in an oilor hydrocarbon solvent, separating the organic phase from the aqueousphase, dividing the aqueous phase into two extracted portions, and usingthe first portion as part of said aqueous solution in step (b) andrecovering the phosphates from the second extracted portion.
 7. In atwo-stage, countercurrent process for recovering phosphates, yttrium andrare earth metal values from apatite, the steps comprising a. leachingsaid material with an aqueous solution containing dissolved phosphateand excess sulfuric acid in an amount sufficient to produce a first acidleach solution containing phosphate and yttrium values from saidmaterial and separating said first acid leach solution from the leachresidue; b. leaching the residue from step (a) with water and sulfuricacid in an amount sufficient to produce a second acid leach liquor witha pH of about 0.02 to about 0.25 containing the residual phosphate,residual yttrium and rare earth values from said material and separatingsaid second acid leach solution from the leached residue; c. recoveringthe yttrium and rare earth values from the second acid leach liquor fromstep (b), by contacting said leach liquor with an organic immisciblesolvent therefor which comprises a suitable amine or alkyl phosphatedissolved in an oil or hydrocarbon solvent, so that during recycling ofsaid second acid leach liquor into step (a), the solubility of theyttrium and rare earth salts will not be exceeded but the phosphatecontent of the solution will be raised to a level sufficient to permitextraction of the phosphate; separating the resulting organic phasecontaining yttrium and rare earth metal values from the aqueous acidphase and recycling the aqueous acid phase to step (a); and d.extracting the yttrium and rare earth values from the first acid leachliquor from step (a) by contacting said leach liquor with an organicimmiscible solvent therefor which comprises a suitable amine or alkylphosphate dissolved in an oil or hydrocarbon solvent, separating theorganic phase from the aqueous phase, dividing the aqueous phase andsending one portion for recovery of the contained phosphate and theother portion to the second stage leach, step (b).